In a fuel cell, a fuel gas supplied to an anode and an oxidizing gas supplied to a cathode react to generate electricity in an electrolyte film, and at the same time as this, moisture is generated. The generated moisture, together with the fuel gas and the oxidizing gas not used for the reaction, is discharged as the exhaust of the fuel cell from a specified exhaust system connected to the fuel cell. In the exhaust system as stated above, there is a case where airflow noise of a relatively high frequency, such as 500 to 2000 Hz, is generated. In order to reduce this airflow noise, a sound absorption type noise eliminator, internally filled with a sound absorption material (sound elimination material), such as glass wool, is often mounted in an exhaust system of a fuel cell vehicle or the like.
The noise eliminator as stated above includes, for example, a sectional structure shown in FIG. 7. This noise eliminator 100 includes an inner pipe 102 through which exhaust from the fuel cell flows, and an outer shell surrounding this, and a sound absorption material 106 such as glass wool is filled between the inner pipe 102 and the outer shell 104. Plural sound transmitting holes 108 are formed in the peripheral wall of the inner pile 102. The sound radiated from the sound transmitting holes 108 to the sound absorption material 106 repeats scattering and interference in the sound absorption material 106, and is attenuated, so that the sound is absorbed by the sound absorption material 106.
A large amount of generated moisture is contained in the exhaust of the fuel cell. There is a case where this moisture is condensed in the inside of the noise eliminator and is dropped or water condensed at the exhaust system upstream side flows into the noise eliminator, and the water is collected in a lower part (hereinafter referred to as a bottom section) in the vertical direction of the noise eliminator. In this case, there is a case where the sound absorption material filled on the bottom section of the noise eliminator adsorbs and holds the water (hereinafter referred to as “contains water”), so that the specified sound absorption performance cannot be exhibited, and the noise eliminating performance of the noise eliminator is lowered.
As prior art to deal with this, for example, JP-A-2002-206413 proposes a noise eliminator 120. As shown in FIG. 8, in the noise eliminator 120, the inside of the noise eliminator 120 is divided up and down in the vertical direction by a partition plate 124 having a continuous hole 122, so that a sound absorption chamber 126 and an expansion chamber 128 are formed. An inner pipe 130 having sound transmitting holes 136 is disposed in the inside of the sound absorption chamber 126, and a sound absorption material is filled so as to surround the inner pipe 130. With this structure, even if the sound absorption material 126 below the inner pipe 130 in the vertical direction contains water, the water can be dropped to the expansion chamber 128 through the continuous hole 122 of the partition plate 124. The water dropped to the expansion chamber 128 is sequentially discharged to the outside of the noise eliminator 120 through a conduit pipe 134.
However, in the noise eliminator shown in FIG. 8, although the water is dropped to the expansion chamber from the sound absorption material at the lower side of the sound absorption chamber, there is a problem that a region where the sound absorption material contains water becomes wide. The water contained in the sound absorption material includes water flowing in from the exhaust system upstream side along the inner wall of the inner pipe, and water condensed on the inner wall of the inner pipe and dropped. The inflow water as stated above is dropped through the sound transmitting holes of the inner pipe and is contained especially in the sound absorption material existing below the inner pipe. The sound absorption material containing water is fibers having a small diameter, such as glass wool, and a gap between the fibers is also usually small. Since the capillarity occurs in the fibers as stated above, there is a case where water is drawn and contained in not only the sound absorption material below and around the inner pipe, but also the sound absorption material above the inner pipe.
As stated above, in the noise eliminator shown in FIG. 8, by the exhaust flow flowing in from the sound transmitting holes of the inner pipe, water can be dropped to the expansion chamber to some extent from the sound absorption material containing water, however, since the region containing water is wide in the filled sound absorption material, it has been difficult for the sound absorption material to exhibit the specified sound absorption performance.
Then, the invention has an object to provide a noise eliminator having such a structure that in a sound absorption material existing in the inside, a region containing water becomes narrow.